docs: def buildfitfcn(self):
          """ Create fit function to fit models in list ``models``. """
          def _fitfcn(p, flatmodels=self.flatmodels):
              ans = gvar.BufferDict()
              for m in flatmodels:
                  ans[m.datatag] = (
                      m.fitfcn(p) if m.ncg <= 1 else
                      MultiFitter.coarse_grain(m.fitfcn(p), m.ncg)
                      )
              return ans
          return _fitfcn